High-power resistors are used in particular for braking electric motors, particularly in thyristor drives, especially high-frequency thyristor drives, but also for many other applications in the field of the control of electric drives. High-power resistors are also required especially in automotive engineering.
Known high-power resistors comprise a wire of a material having an electric resistance, which is wound around a core, the core generally being able to withstand high temperatures. There are also known high-power resistors made of a spiral wire which is not wound around a core. The wire is provided with an electric insulation. It is disposed in a thermally conductive material surrounded by a metallic housing which acts as heat exchanger.
In the known high-power resistors problems arise in particular when the operating frequency is high, for instance higher than 1 kHz, and/or when it is important to maintain the wave shape of the current. In the known power resistors the problems arise in particular as a result of the fact that they have a certain capacity and/or inductance by virtue of their construction, by which the shape and the format of the voltage signal and/or the current signal, which can for instance be rectangular or sinusoidal, can be impaired in an undesirable way.
It is an object of the present invention to provide an improved high-power resistor.
In accordance with the present invention, this object is solved by the features of claims 1 and 10. The high-power resistor comprises a housing which can be or is traversed by a cooling medium and in which a resistance element is provided. The cooling medium can be liquid or gaseous. Preferably, the cooling medium is liquid.
Advantageous embodiments are described in the dependent claims.
Preferably, the resistance element is planiform.
In the housing, a plurality of resistance elements, preferably three, can be provided. The resistance elements can be connected in parallel or in series. It is particularly advantageous when a plurality of planiform resistance elements are provided, which are arranged parallel to each other.
Preferably, separators are provided between the resistance elements. By means of the separators, the resistance elements can be isolated from each other. Furthermore, the separators can serve as conducting devices for the cooling medium. A particularly simple solution is obtained when planiform resistance elements are separated from each other by planiform separators.
Another advantageous embodiment is characterized in that the housing is made of plastic material, preferably of thermoplastic material. Such housing can be manufactured at low cost.
At the housing, connections can be provided, in particular tube connections for supplying and discharging the cooling medium.
Preferably, a terminal box is provided at the housing. The terminal box can include electric contacts for connecting electric lines.
Another advantageous embodiment is characterized by sealed connections for connecting the resistance element with the terminal box.
The present invention furthermore relates to a resistance unit which consists of a plurality of high-power resistors.
According to the embodiments described in the present application, a cooling-medium-cooled, in particular liquid-cooled high-power resistor is created. It provides for realizing a resistor with high performance values and in particular with low impedance and low induction. Particularly advantageously, the high-power resistor can be used for braking electric motors, in particular in high-frequency thyristor drives, but also in many other applications in the field of electric drive engineering, in particular the control of electric drives. Another important field of application is automotive engineering.
In particular in fields of application in which a low weight and/or a high packing density of the electric and/or electronic components is decisive, especially in the automotive industry, it is desirable to achieve a rather high power dissipation. This is required in particular during hard braking operations. At the same time, the required space should be minimized. The embodiments of the present invention provide for solving these problems.